Mechanical double joint system

ABSTRACT

An exemplary mechanical joint system ( 100 ) includes a joint ( 10 ), an arm ( 20 ), a plurality of teeth ( 211 ), and an engaging member ( 3 ). The arm is rotatable relative to the joint. A pivot hole ( 210 ) is defined in the arm. The teeth are formed on an inner surface adjacent to an end of the pivot hole. The engaging member is fixed to the joint. The engaging member includes a prong ( 323 ) for engaging with the teeth.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to rotatable joints, and moreparticularly, to a mechanical double joint system.

2. Discussion of the Related Art

Rotatable joints accommodates movement for arms of mechanical devices.As such, a mechanical device, having an arm designed for movement,includes a rotatable joint. The rotatable joint may join an arm or anactuating portion to a supporting portion (generally the body) of themechanical device. In other words, the actuating portion is attached tothe supporting portion by the rotatable joint. A typical actuatingportion includes a base fixed to the supporting portion, a movablemember fixed to the actuating portion, and a pivot shaft for connectingthe base and the movable member. A pivot hole is defined in the base,and an end of the pivot shaft is rotatably engaged in the pivot hole.The other end of the pivot shaft is rotatably connected to the movablemember by a pin. Thus, the movable member not only can rotate togetherwith the pivot shaft relative to the base, but can also rotate relativeto the pivot shaft.

Due to frictional force, wear and tear of usage, the pivot shaft and thepin of the rotatable joint may become worn out, thus the rotatable jointmay become unstable and control of the actuating portion may suffer.

Therefore, a mechanical double joint system that is less likely to beworn out, and to be stable over the long term, is desired.

SUMMARY

In one aspect, a mechanical joint system includes a first joint member,an arm, a plurality of teeth, and a grasping element. The arm isrotatable relative to the first joint member. A pivot hole therein isdefined in the arm. The teeth are formed on an inner surface adjacent toan end of the pivot hole. The engaging member is fixed to the firstjoint member. The engaging member includes a prong for engaging with theteeth.

In another aspect, a mechanical joint system includes a first jointmember, an arm, a grasping element, and a latching element. The arm isrotatable relative to the first joint member. A pivot hole is defined inthe arm. The engaging member is fixed to the first joint member. Theengaging member includes a plurality of teeth extending from outersurface thereof. The latching member is mounted in the pivot hole forengaging with the teeth.

Other advantages and novel features will become more apparent from thefollowing detailed description when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the drawings are not necessarily drawn to scale, theemphasis instead being placed upon clearly illustrating the principlesof the present mechanical double joint system. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views, and all the views are schematic.

FIG. 1 is an assembled, isometric view of a mechanical double jointsystem in accordance with a first embodiment of the present invention.

FIG. 2 is an exploded, isometric view of the mechanical double jointsystem shown in FIG. 1.

FIG. 3 is an isometric view of a first joint member of the mechanicaldouble joint system shown in FIG. 1.

FIG. 4 is an isometric view of an arm of the mechanical double jointsystem shown in FIG. 1.

FIG. 5 is a cross-sectional view of the mechanical double joint systemshown in FIG. 1, taken along line V-V thereof.

FIG. 6 is an enlarged view of an encircled portion VI shown in FIG. 1.

FIG. 7 is isometric view of an engaging member of a mechanical doublejoint system in accordance with a second embodiment of the presentinvention.

FIG. 8 is isometric view of an engaging member of a mechanical doublejoint system in accordance with a third embodiment of the presentinvention.

FIG. 9 is isometric view of an arm of the mechanical double joint systemin accordance with the third embodiment of the present invention.

FIG. 10 is partially, cross-sectional view of the engaging memberengaging with the arm of the mechanical double joint system inaccordance with the third embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made to the drawings to describe preferredembodiments of the present mechanical double joint system in detail.

Referring to FIG. 1, a mechanical double joint system 100 in accordancewith a first embodiment is shown. The mechanical double joint system 100includes a first joint member 10, an arm 20, an engaging member 3, and asecond joint member 40. The arm 20 is rotatable relative to the firstjoint member 10. The second joint member 40 is rotatable relative to thearm 20.

Referring also to FIGS. 2 through 4, a pivot hole 101 and a firstreceiving slot 102 are defined in the first joint member 10. The pivothole 101 communicates with the first receiving slot 102. The first jointmember 10 further includes a first flange portion 121 and a secondflange portion 122 formed in the pivot hole 101. The first flangeportion 121 is adjacent to a first sidewall in the first receiving slot102 and the second flange portion 122 is adjacent to a second oppositesidewall in the first receiving slot 102. A plurality of locking grooves123 are defined in the second flange portion 122.

The arm 20 is substantially a shaft including a pivot portion 21disposed at an end thereof and a ball 22 disposed at another endthereof. The pivot portion 21 is substantially a cylinder with a pivothole 210 defined through a center thereof. The pivot portion 21 furtherincludes a plurality of teeth 211 formed on an inner surface adjacent toan end of the pivot hole 210. An engaging flange 212 is protruded outfrom an inner surface adjacent to another end of the pivot hole 210. Aplurality of shaft positioning prong grooves 213 are defined in theengaging flange 212. The ball 22 is configured for rotatably engaging inthe second joint member 40.

Each of the teeth 211 is preferred to be an elongated protrusion. Across-section of elongated protrusion is preferred to be V-shaped orsemicircular.

The engaging member 3 includes a pivot shaft 31 and a pivot shaftpositioner 32. The pivot shaft 31 includes a shaft head 311 and a shaftportion 312 extending from an end of the shaft head 311. The shaft head311 has a size corresponding to that of the pivot hole 101 of the firstjoint member 10. A length of the shaft head 311 is equal to a length ofa portion of the pivot hole 101 between an inner end surface of thefirst flange portion 121 and an outer end surface of the first jointmember 10. Thus, when the shaft head 311 is received in the pivot hole101, an outer end surface of the shaft head 311 and the outer endsurface of the first joint member 10 are substantially coplanar. Aflange 313 is formed at the end of the shaft portion 312. The shaftportion 312 defines four first axial slots 314 therein along a directionparallel to an axis of the shaft portion 312. The pivot shaft positioner32 includes a shaft head 321 and four latching rims 322. The latchingrims 322 are configured to engage in the first axial slots 314 of thepivot shaft 31 correspondingly. The shaft head 321 has a sizecorresponding to that of the pivot hole 101 of the first joint member10. A length of the shaft head 321 is equal to a length of a portion ofthe pivot hole 101 between an inner end surface of the second flangeportion 122 and an outer end surface of the first joint member 10. Thus,when the shaft head 321 is received in the pivot hole 101, an outer endsurface of the shaft head 321 and the outer end surface of the firstjoint member 10 are substantially coplanar. Each of the latching rims322 includes a prong 323 formed at an end thereof. The pivot shaft 31and the pivot shaft positioner 32 are deformable along a radialdirection of the pivot shaft 31 and the pivot shaft positioner 32.

Each of the prongs 323 is preferred to be an elongated protrusion. Across-section of the prongs 323 is preferred to be V-shaped orsemicircular.

It should be understood that, the number of the first axial slots 314and the number of the latching rims 322 are not limited to four. Thenumber of the first axial slots 314 and the number of the latching rims322 are preferred to be at least two. The first axial slots 314 areevenly defined on the pivot shaft 31. The latching rims 322 are evenlyformed on the pivot shaft positioner 32.

The second joint member 40 includes a first half 401 and a second half402 that collectively form the second joint member 40. The first half401 includes a plurality of cylindrical poles perpendicularly extendingfrom an inner surface thereof. Each of the cylindrical poles defines acircular hole 411 therein. The second half 402 includes a plurality oflatching poles 412 perpendicularly extending from an inner surfacethereof. Each of the latching poles 412 has a size corresponding to oneof the circular holes 411 of the cylindrical poles, thus the first half401 and the second half 402 can be held together by inserting thelatching poles 412 into the circular holes 411 correspondingly. A radiusof each latching pole 412 is the same as or a little larger than aradius of each circular hole 411, thus each of the latching poles 412 isable to tightly engage in one of the circular hole 411. The second jointmember 40 defines a restricting hole 413 at an end thereof. Half of therestricting hole 413 is defined in an end of the first half 401 and theother half of the restricting hole 413 is defined in a corresponding endof the second half 402. The first half 401 and the second half 402 bothinclude a socket holder 415 having a plurality of fixing piecesextending from an inner surface thereof.

The mechanical double joint system 100 further includes a socket havinga first half and a second half sockets 50. Each of the first and secondhalf sockets 50 includes a concave inner surface 501. The concave innersurface 501 is substantially spherical surface. The concave innersurfaces 501 of the first and second half sockets 50 are orientedsymmetrically opposite to each other for cooperatively clamping the ball22 of the arm 20. Each of the first and second half sockets 50 defines aplurality of latching grooves 511 at an outer surface thereof forengaging with the fixing pieces of the socket holder 415 of the secondjoint member 40. The first and second half sockets 50 can be fixed tothe first half 401 and the second half 402 correspondingly by insertingthe first and second half sockets 50 into the socket holder 415.

In an alternative embodiment, One of the first and second half sockets50 is welded to the first half 401 and the other of the first and secondhalf sockets 50 is welded to the second half 402. It should beunderstood that, the first and second half sockets 50 can also be madeintegrally with the first half 401 and the second half 402correspondingly.

To assemble the mechanical double joint system 100, the pivot portion 21of the arm 20 is received in the first receiving slot 102 of the firstjoint member 10. The pivot hole 210 of the arm 20 and the pivot hole 101of the first joint member 10 are aligned along a same axis.

The pivot shaft 31 of the engaging member 3 is inserted into the pivothole 101 of the first joint member 10 and the pivot hole 210 of the arm20 from such end of the pivot hole 101 which has the first flangeportion 121. The flange 313 of the pivot shaft 31 is compressed along aradial direction of the flange 313 by the engaging flange 212 whenextends through the engaging flange 212. After the whole flange 313extending through the engaging flange 212, the flange 313 rebound to itsoriginal position, thereby preventing the pivot shaft 31 detaching fromthe pivot hole 101 of the first joint member 10.

Each of the first axial slots 314 of the pivot shaft 31 aims at onecorresponding shaft-positioning prong groove 213 of the engaging flange212 which aims at one corresponding locking groove 123 of the secondflange portion 122. The pivot shaft positioner 32 is inserted into thepivot hole 101 of the first joint member 10 and the pivot hole 210 ofthe arm 20 from such end of the pivot hole 101 which has the secondflange portion 122. The latching rims 322 of the pivot shaft positioner32 run through the locking grooves 123 of the second flange portion 122and the shaft-positioning prong groove 213 of the engaging flange 212,and are inserted into the first axial slots 314 of the pivot shaft 31correspondingly. The prongs 323 of the latching rims 322 extend out ofthe first axial slots 314 of the pivot shaft 31 for engaging with theteeth 211 of the arm 20. The arm 20 are rotated so that each of theshaft-positioning prong grooves 213 of the engaging flange 212 does notaim at one corresponding prong 323 of each latching rim 322, therebypreventing the pivot shaft positioner 32 detaching from the first jointmember 10.

The first and second half sockets 50 are fixed to the first half 401 andthe second half 402 correspondingly by inserting the first and secondhalf sockets 50 into the socket holders 415. The concave inner surfaces501 of the first and second half sockets 50 are oriented symmetricallyopposite to each other and cooperatively clamp the ball 22 of the arm20. The first half 401 is attached to the second half 402 by insertingthe latching poles 412 into the circular holes 411 correspondingly tocollectively form the second joint member 40. Then, the mechanicaldouble joint system 100 is assembled.

Referring also to FIGS. 5 and 6, to use the mechanical double jointsystem 100, the arm 20 is rotatable relative to the engaging member 3.The engaging member 3 is fixed relative to the first joint member 10,thus the arm 20 is also rotatable relative to the first joint member 10.The latching rims 322 of the pivot shaft positioner 32 have radialelasticity, thus the prong 323 of the latching rims 322 are able to bepressed down along the radial direction of the grasping shaft 32 and canalso rebound to an original position. When an external force is appliedto the arm 20, the teeth 211 of the arm 20 will press the prongs 323 ofthe latching rims 322 into the first axial slots 314 of the pivot shaft31, thus the arm 20 is rotated. With no external force on the arm 20,each of the prongs 323 of the latching rims 322 retains between twoadjacent teeth 211 of the arm 20, thus the arm 20 can stably retain aposition relative to the first joint member 10. In addition, each of theprongs 323 can retain between any two adjacent teeth 211 of the arm 20,thus the arm 20 can stably retain at several different positionsrelative to the first joint 10 member.

The second joint member 40 engages with the ball 22, thus the secondjoint member 40 is able to rotate relative to the arm 20. Frictionalforce produced between the concave inner surfaces 501 of the first andsecond half sockets 50 and the ball 22 of the arm 20 can make the secondjoint member 40 retain a stable position relative to the arm 20. Itshould be understood that, the range for rotating the second jointmember 40 is determined by the size of the restricting hole 413 of thesecond joint member 40. If the size of the restricting hole 413 isrelative large, the second joint member 40 is able to be swung orrotated in a relatively large range. Otherwise, if the size of therestricting hole 413 is relatively small, the second joint member 40 isable to be swung or rotated in a relatively small range.

In alternative embodiments, the arm 20 is directly fixed to a part of amechanical device by one of means of melting, rivet, or glue. Inaddition, the arm 20 can also be made integrally with a part of amechanical device. In that case, the ball 22, the second joint member40, and the first and second half sockets 50 are omitted accordingly.

Referring to FIG. 7, an engaging member 4 according to a secondembodiment is shown. The engaging member 4 includes a fixing member 41and a pivot shaft 42. The pivot shaft 42 includes a shaft head 421, ashaft portion 422 extending from an end of the shaft head 421, and fourlatching rims 423. The latching rims 423 circle an end of the shaftportions 422 and are connected to an end of the shaft head 421. Theshaft portion 422 defines a threaded hole 424 in an end opposite to theshaft head 421 and at least one U-shaped groove 425 in a middle portionthereof. The U-shaped groove 425 communicates with the threaded hole424, thereby forming an elastic plate 426 connecting to the shaftportion 422. The elastic plate 426 includes a prong 427 extending froman outer surface of the elastic plate 426. The fixing member 41 includesa shaft head 411 and a thread portion 412 extending from an end of theshaft head 411. The threaded portion 412 is configured to screw into thethreaded hole 424.

The pivot shaft 42 and the fixing member 41 are assembled to a firstjoint member from two end of a pivot hole of the first joint member. Thefixing member 41 is fixed to the pivot shaft 42 with the threadedportion 412 screwed into the threaded hole 424 of the pivot shaft 42.The pivot shaft 42 is fixed relative to the first joint member when thelatching rims 423 are received in locking grooves of the first jointmember. The shaft portion 422 is received in a pivot hole of an arm andthe prong 427 of the shaft portion 422 engage between two adjacent teethof the arm.

Because the elastic plate 426 has elasticity, thus the elastic plate 426is able to be compressed along the radial direction of the shaft portion422 and can also rebound to an original position. When an external forceis applied to the arm, teeth of the arm will press the prongs 427 of theelastic plate 426 downwards, thus the arm is rotated. When the externalforce is canceled from the arm, the prong 427 of the shaft portion 422retains between two adjacent teeth of the arm, thus the arm can retain astable position relative to the first joint member.

Referring to FIG. 8, an engaging member 5 according to a thirdembodiment is shown. The engaging member 5 includes a pivot shaft 52 anda fixing member 51. The pivot shaft 52 includes a shaft head 521, ashaft portion 522 extending from an end of the shaft head 521, and fourlatching rims 523. The latching rims 523 circles an end of the shaftportions 522 and are connected to an end of the shaft head 521. Theshaft portion 522 defines a threaded hole 524 in an end opposite to theshaft head 521. The shaft portion 422 includes a plurality of teeth 525extending from a middle portion thereof. The fixing member 51 includes ashaft head 511 and a thread portion 512 extending from an end of theshaft head 511. The threaded portion 512 is configured to screw into thethreaded hole 524.

The pivot shaft 52 and the fixing member 51 are assembled to a firstjoint member from two end of a pivot hole of the first joint member. Thefixing member 51 is fixed to the pivot shaft 52 with the threadedportion 512 screwed into the threaded hole 524 of the pivot shaft 52.The pivot shaft 52 is fixed relative to the first joint member when thelatching rims 523 are received in locking grooves of the first jointmember.

Referring to FIG. 9, an arm 60 according to the third embodiment isshown. The arm 60 is substantially a shaft including a pivot portion 61and a ball (not labeled) opposite to the pivot portion 61. The pivotportion 61 defines a pivot hole 610 in a center thereof. The pivotportion 61 further includes a plurality of latching elements 611 mountedin the pivot hole 610.

Referring to FIG. 10, the pivot portion 61 defines a plurality ofnon-through holes 612 in an inner surface of the pivot hole 610. Each ofthe latching elements 611 is a steel ball received in a non-through hole612 of the pivot portion 61. A compressed spring 613 is also received ineach of the non-through hole 612. An end of the compressed spring 613 isfixed to a bottom surface of the non-through hole 612 and an oppositeend of the compressed spring 613 is fixed to a latching member 611.

Each of the latching elements 611 is able to be pressed into one of thenon-through holes of the pivot portion 61 and can also be rebounded toan original position by the compressed spring 613. When an externalforce is applied to the arm 60, each of latching elements 611 is pressedinto one of the non-through holes of the pivot portion 61, thus the arm60 is able to be rotated. When the force is canceled from the arm 60,each of latching elements 611 retains between two adjacent teeth of thearm, thus the arm 60 can retain a stable position relative to the firstjoint member.

It should be understood that, the mechanical double joint system 100 isnot limited to use for mechanical device, it can also be used forconnecting an actuating portion and a supporting portion of othersimilar devices.

It is believed that the present embodiments and their advantages will beunderstood from the foregoing description, and it will be apparent thatvarious changes may be made thereto without departing from the spiritand scope of the invention or sacrificing all of its materialadvantages, the examples hereinbefore described merely being preferredor exemplary embodiments of the invention.

1. A mechanical joint system, comprising: a first joint member defininga pivot hole extending through a first flange portion and a secondflange portion in perpendicular communication with a receiving slot thatextends between the first and second flange portions; the second flangeportion defining a plurality of locking grooves; an arm being rotatablerelative to the first joint member and having a pivot portion pivotablyreceived within the receiving slot of the first joint member, the pivotportion defining a pivot hole extending therethrough and being axiallyaligned with the pivot hole of the first joint member, the pivot hole ofthe pivot portion having a plurality of teeth formed on an inner surfaceadjacent to an end of the pivot hole of the pivot portion and aplurality of shaft positioning prong grooves defined in the innersurface adjacent to another end of the pivot hole of the pivot portion;and an engaging member received through the aligned pivot holes of thefirst joint member and the pivot portion of the arm, the engaging membercomprising: a pivot shaft inserted in the pivot hole of the first jointmember from an end thereof, and comprising a shaft head and a shaftportion extending from an end of the shaft head; the shaft portiondefining a plurality of axial slots therein along a direction parallelto an axis of the shaft portion; and a pivot shaft positioner insertedin the pivot hole of the first joint member from an opposite endthereof, and the pivot shaft positioner comprising a shaft head and aplurality of latching rims extending from an end of the shaft head toengage in the locking grooves of the first joint member, the shaftpositioning prong grooves, and finally engage into the axial slots ofthe pivot shaft correspondingly; wherein, each latching rim has a pronglatching with one of the plurality of teeth of the arm, when an externalforce is applied to the arm, the plurality of teeth press the prongsinto the axial slots to allow the arm to rotate relative to the firstjoint member.
 2. The mechanical joint system as claimed in claim 1,wherein the pivot shaft and the pivot shaft positioner are deformablealong a radial direction of the pivot shaft and the pivot shaftpositioner.
 3. The mechanical double joint system as claimed in claim 1,wherein each prong is an elongated protrusion formed on one end of thecorresponding each latching rim, and a cross-section of the elongatedprotrusion is V-shaped.
 4. The mechanical joint system as claimed inclaim 1, wherein the first flange portion and the second flange portionare disposed adjacent to opposite sides of the receiving slotcorrespondingly.
 5. The mechanical joint system as claimed in claim 1,further comprising a second joint member, the second joint memberincluding a first half and a second half attached to the first half, thearm further comprising a ball opposite to the pivot portion forrotatably engaging in the second joint member.
 6. The mechanical jointsystem as claimed in claim 5, wherein the first half comprises aplurality of cylindrical poles extending from an inner surface thereof,each of the cylindrical poles defines a circular hole therein, thesecond half includes a plurality of latching poles extending from aninner surface thereof, each of the latching poles has a sizecorresponding to one of the circular holes, the first half is attachedto the second half by inserting the latching poles into the circularholes correspondingly.
 7. The mechanical joint system as claimed inclaim 5, further comprising a pair of first and second half sockets,each of the first and second half sockets including a concave innersurface, the first and second half sockets fixed to the first half andthe second half correspondingly, and the concave inner surfaces beingoriented symmetrically opposite to each other to cooperatively clamp theball of the arm.
 8. A mechanical joint system, comprising: a first jointmember defining a pivot hole and a receiving slot communicating with thepivot hole; an arm being rotatable relative to the first joint member,the arm having a pivot portion pivotably received within the receivingslot of the first joint member, and defining a pivot hole through thepivot portion axially aligned with the pivot hole of the first jointmember; an engaging member fixed to the first joint member andcomprising a pivot shaft and a fixing member; the pivot shaft fixedlyreceived within the pivot hole of the first joint member from an endthereof, and comprising a shaft head, a shaft portion extending from anend of the shaft head and a plurality of teeth extending from outersurface of the shaft portion; the fixing member received within thepivot hole of the first joint member from an opposite end thereof, andfixed relative to the pivot shaft; and at least one latching membermounted in the pivot hole of the arm for engaging with the teeth of theshaft portion of the pivot shaft; wherein, the arm has a first end pivotportion with a first cylindrical pivot hole extending there through, thehole having radially inward pointing teeth, radially inward pointingengaging flange having a plurality of shaft positioning prong groovesthere through; the first joint member has a second cylindrical pivothole extending through a first inner flange and a second inner flange inperpendicular communication with a receiving opening that extendsbetween the flanges, the receiving hole receiving the pivot portionpivotally therein such that the first and second pivot holes are inaxially aligned communication, the second flange having locking grooves;the engaging member is received through the aligned pivot holes, andthat the engaging member has a shaft head at a first end, a shaftportion with slots there through, and a flange at a second end; a pivotshaft positioner received through the aligned pivot holes, the shaftpositioner having a shaft head at a first end and latching rims at asecond end, each rim having a prong, the rims received through thelocking grooves, the shaft positioning prong grooves, and the slots suchthat the prongs latch with the teeth; when an external force is appliedto the arm the teeth press the prongs into the slots to allow the arm torotate relative to the first joint member.
 9. The mechanical jointsystem as claimed in claim 8, wherein the shaft portion of the pivotshaft defines threaded hole in an end opposite to the shaft head of thepivot shaft, the fixing member includes a shaft head and a threadedportion extending from an end of the shaft head, the fixing member isfixed to the pivot shaft with the threaded portion engaged in thethreaded hole of the pivot shaft.
 10. The mechanical joint system asclaimed in claim 8, further comprising a second joint member, the secondjoint member including a first half and a second half attached to thefirst half, the arm further comprising a ball opposite to the pivotportion to rotatably engage in the second joint member.
 11. A mechanicaljoint system, comprising: a first joint member defining a pivot holeextending through a first flange portion and a second flange portion inperpendicular communication with a receiving slot that extends betweenthe first and second flange portions; an arm being rotatable relative tothe first joint member and having a pivot portion pivotably receivedwithin the receiving slot of the first joint member, the pivot portiondefining a pivot hole extending therethrough and being axially alignedwith the pivot hole of the first joint member, the pivot hole of thepivot portion having a plurality of teeth formed on an inner surfaceadjacent to an end of the pivot hole of the pivot portion; and anengaging member received through the aligned pivot holes of the firstjoint member and the pivot portion of the arm; and a pivot shaftpositioner inserted in the pivot hole of the first joint member from anopposite end thereof; wherein, the arm has a first end pivot portionwith a first cylindrical pivot hole extending there through, the holehaving radially inward pointing teeth, radially inward pointing engagingflange having a plurality of shaft positioning prong grooves therethrough; the first joint member has a second cylindrical pivot holeextending through a first inner flange and a second inner flange inperpendicular communication with a receiving opening that extendsbetween the flanges, the receiving hole receiving the pivot portionpivotally therein such that the first and second pivot holes are inaxially aligned communication, the second flange having locking grooves;the engaging member is received through the aligned pivot holes, andthat the engaging member has a shaft head at a first end, a shaftportion with slots there through, and a flange at a second end; a pivotshaft positioner received through the aligned pivot holes, the shaftpositioner having a shaft head at a first end and latching rims at asecond end, each rim having a prong, the rims received through thelocking grooves, the shaft positioning prong grooves, and the slots suchthat the prongs latch with the teeth; when an external force is appliedto the arm the teeth press the prongs into the slots to allow the arm torotate relative to the first joint member.